The present invention relates to a liquid drain system. In particular, the present invention relates to a water drain system for removing water separated in a fuel filter within a liquid fuel supply system. The fuel supply system may in particular be part of a vehicle, and more particularly, a diesel truck.
Fuel supply systems, and in particular vehicle fuel systems generally comprise at least one fuel filter to remove water and other contaminants from the fuel. For medium and heavy duty trucks, there is generally a need for multiple fuel filters, for instance a pre-filter for separating out water on the suction side (that is, upstream of the main fuel pump) and for removing large particulate contaminants and a final filter for removing fine particles on the pressure side (that is, downstream of the main fuel pump). It is generally necessary to continuously or periodically remove the separated water from the fuel filter in order to prevent water passing through the filter element into the fuel system and therefore reaching the engine injector nozzles. The filter media also needs to be changed at the regular intervals as it becomes clogged by contaminants leading to high pressure drop across the primary filter.
It is possible to filter water from the fuel supply and extract the water on the pressure side. However, it is undesirable to do so as the main fuel pump is not protected from the presence of water in the fuel supply. Additionally, due to the increased flow rates on the pressure side, water separation is more difficult and consequently the fuel filter and the water drain may be more expensive. If water is to be separated on the pressure side then water may be drained using a solenoid fuel drain valve. As the separated water is pressurised by the pressurised fuel, the solenoid fuel drain valve requires no additional pressurisation or air inlet in order to function.
It is generally more cost effective and efficient to separate water from fuel on the suction side (that is, the portion of the fuel system that is not pressurised as it is upstream of the main fuel pump). This is particularly the case for diesel applications. Draining of the separated water on the suction side may either be done manually or automatically using a solenoid fuel drain valve. Known manual fuel drain valves for fuel filters on the suction side allow water which has been separated from the fuel supply to be released. The water may either be collected in a separate receptacle or allowed to drain away. The operator of a manual fuel drain valve periodically releases the water, and any other contaminants present, by rotating the manual drain valve. If during water draining operation the primary fuel filter is not pressurised by an additional pump (for instance a priming pump), a manual self-venting valve may be used. Water drains through a first hole as air enters the fuel filter through a second hole in the valve.
Manual water drain systems are frequently positioned in a position within the engine bay which is not easily accessed. Additionally, manual draining of water is inconvenient for the operator and if neglected can cause water to pass through the fuel filter media and enter the fuel system causing damage to the engine injector nozzles thereby reducing life of the engine.
As an alternative to manual water drain systems, solenoid activated water drain valves have been developed. Solenoid fuel drain valves are electrically operated. Operation may be controlled manually, for instance by activation of a switch within the vehicle cabin by the operator of the vehicle in response to a warning signal that water is present in the fuel filter. A problem associated with some conventional types of solenoid fuel drain valves is that the primary filter needs to be pressurised in order to expel water through the valve. This requires the provision of an additional electrical pump, which increases the cost of the filter.
PCT patent publication number WO-2004/007942 discloses an improved solenoid water drain valve which needs not be positioned below the fuel tank to provide the necessary pressurisation, and is not provided with separate pressurisation means. The solenoid fuel drain valve is arranged to be operated when the engine is not in operation to allow water and other contaminants to flow from the fuel filter. Air vent holes are provided within the solenoid valve allowing for self venting in which as water drains away it is replaced by air. If the filtering system is generally under suction, the improved solenoid water drain valve operates by reducing and ultimately eliminating the pressure differential between the water collection vessel and the ambient environment thereby enabling the valve to drain. Even in the presence of pressure within the filter, and therefore a significant pressure differential, the improved solenoid valve can still function efficiently and provide significantly better performance than conventional solenoid valves, which will not drain when under suction or when the pressure differential across the valve zero. Air within the primary filter can be expelled using the existing air vent valve.
However, as the improved solenoid fuel drain valve still needs to be operated by the vehicle operator there remains a chance that the operator may forget, or fail to dispose of the water correctly, risking damage to the remainder of the fuel system and the engine, in particular the injector nozzles. Additionally, the solenoid drain valve releases some fuel along with the water, which unless collected and disposed of correctly is a source of pollution.
It is an object of embodiments of the present invention to obviate one or more of the problems associated with the prior art, whether identified herein or elsewhere. In particular, it is an object of embodiments of the present invention to provide a water drain system which is suitable for operating on the suction side of a fuel supply and which eliminates the requirement for the involvement of a vehicle's operator. It is an object of certain embodiments of the present invention to provide such a water drain system suitable for coupling to means for disposing of the water through the vehicle's hydrocarbon (HC) dosing system.